Metabolizable Semiconducting Polymer Nanoparticles for Second Near‐Infrared Photoacoustic Imaging

Photoacoustic (PA) imaging in the second near‐infrared (NIR‐II) window (1000–1700 nm) holds great promise for deep‐tissue diagnosis due to the reduced light scattering and minimized tissue absorption; however, exploration of such a noninvasive imaging technique is greatly constrained by the lack of biodegradable NIR‐II absorbing agents. Herein, the first series of metabolizable NIR‐II PA agents are reported based on semiconducting polymer nanoparticles (SPNs). Such completely organic nanoagents consist of π‐conjugated yet oxidizable optical polymer as PA generator and hydrolyzable amphiphilic polymer as particle matrix to provide water solubility. The obtained SPNs are readily degraded by myeloperoxidase and lipase abundant in phagocytes, transforming from nonfluorescent nanoparticles (30 nm) into NIR fluorescent ultrasmall metabolites (≈1 nm). As such, these nanoagents can be effectively cleared out via both hepatobiliary and renal excretions after systematic administration, leaving no toxicity to living mice. Particularly these nanoagents possess high photothermal conversion efficiencies and emit bright PA signals at 1064 nm, enabling sensitive NIR‐II PA imaging of both subcutaneous tumor and deep brain vasculature through intact skull in living animals at a low systematic dosage. This study thus provides a generalized molecular design toward organic metabolizable semiconducting materials for biophotonic applications in NIR‐II window.     

A convenient preparation of multi-spectral microparticles by bacteria-mediated assemblies of conjugated polymer nanoparticles for cell imaging and barcoding

A novel technique was developed for preparing encoded multicolour microparticles based on the self-assembly of bacteria and conjugated polymer nanoparticles (CPNs) by a very simple and time-saving manner. These bacteria-CPNs microparticles show multicolor emissions by tuning FRET efficiencies among CPNs under single excitation wavelength and can be successfully applied for cell imaging and optical barcoding.     

Multifunctional Conjugated Polymer Nanoparticles for Image‐Guided Photodynamic and Photothermal Therapy

A multifunctional theranostic platform based on conjugated polymer nanoparticles (CPNs) with tumor targeting, fluorescence detection, photodynamic therapy (PDT), and photothermal therapy (PTT) is developed for effective cancer imaging and therapy. Two conjugated polymers, poly[9,9‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)‐ethyl)fluorenyldivinylene]‐alt‐4,7‐(2,1,3‐benzothiadiazole) with bright red emission and photosensitizing ability and poly[(4,4,9,9‐tetrakis(4‐(octyloxy)phenyl)‐4,9‐dihydro‐s‐indacenol‐dithiophene‐2,7‐diyl)‐alt‐co‐4,9‐bis(thiophen‐2‐yl)‐6,7‐bis(4‐(hexyloxy)phenyl)‐thiadiazolo‐quinoxaline] with strong near‐infrared absorption and excellent photothermal conversion ability are co‐loaded into one single CPN via encapsulation approach using lipid‐polyethylene glycol as the matrix. The obtained co‐loaded CPNs show sizes of around 30 nm with a high singlet oxygen quantum yield of 60.4% and an effective photothermal conversion efficiency of 47.6%. The CPN surface is further decorated with anti‐HER2 affibody, which bestows the resultant anti‐HER2‐CPNs superior selectivity toward tumor cells with HER2 overexpression both in vitro and in vivo. Under light irradiation, the PDT and PTT show synergistic therapeutic efficacy, which provides new opportunities for the development of multifunctional biocompatible organic materials in cancer therapy.     

A Porphyrin‐Based Conjugated Polymer for Highly Efficient In Vitro and In Vivo Photothermal Therapy

Conjugated polymers have been increasingly studied for photothermal therapy (PTT) because of their merits including large absorption coefficient, facile tuning of exciton energy dissipation through nonradiative decay, and good therapeutic efficacy. The high photothermal conversion efficiency (PCE) is the key to realize efficient PTT. Herein, a donor–acceptor (D–A) structured porphyrin‐containing conjugated polymer (PorCP) is reported for efficient PTT in vitro and in vivo. The D–A structure introduces intramolecular charge transfer along the backbone, resulting in redshifted Q band, broadened absorption, and increased extinction coefficient as compared to the state‐of‐art porphyrin‐based photothermal reagent. Through nanoencapsulation, the dense packing of a large number of PorCP molecules in a single nanoparticle (NP) leads to favorable nonradiative decay, good photostability, and high extinction coefficient of 4.23 × 10⁴m ^?1 cm^?1 at 800 nm based on porphyrin molar concentration and the highest PCE of 63.8% among conjugated polymer NPs. With the aid of coloaded fluorescent conjugated polymer, the cellular uptake and distribution of the PorCP in vitro can be clearly visualized, which also shows effective photothermal tumor ablation in vitro and in vivo. This research indicates a new design route of conjugated polymer‐based photothermal therapeutic materials for potential personalized theranostic nanomedicine.     

Aromatic‐Diimide‐Based n‐Type Conjugated Polymers for All‐Polymer Solar Cell Applications

All‐polymer solar cells (all‐PSCs) have attracted immense attention in recent years due to their advantages of tunable absorption spectra and electronic energy levels for both donor and acceptor polymers, as well as their superior thermal and mechanical stability. The exploration of the novel n‐type conjugated polymers (CPs), especially based on aromatic diimide (ADI), plays a vital role in the further improvement of power conversion efficiency (PCE) of all‐PSCs. Here, recent progress in structure modification of ADIs including naphthalene diimide (NDI), perylene diimide (PDI), and corresponding derivatives is reviewed, and the structure–property relationships of ADI‐based CPs are revealed.     

Ultrastable Near‐Infrared Conjugated‐Polymer Nanoparticles for Dually Photoactive Tumor Inhibition

It is highly desired that satisfactory photoactive agents with ideal photophysical characteristics are explored for potent cancer phototherapeutics. Herein, bifunctional nanoparticles of low‐bandgap donor–acceptor (D–A)‐type conjugated‐polymer nanoparticles (CP‐NPs) are developed to afford a highly efficient singlet‐to‐triplet transition and photothermal conversion for near‐infrared (NIR) light‐induced photodynamic (PDT)/photothermal (PTT) treatment. CP‐NPs display remarkable NIR absorption with the peak at 782 nm, and perfect resistance to photobleaching. Photoexcited CP‐NPs undergo singlet‐to‐triplet intersystem crossing through charge transfer in the excited D–A system and simultaneous nonradiative decay from the electron‐deficient electron acceptor isoindigo derivative under single‐wavelength NIR light irradiation, leading to distinct singlet oxygen quantum yield and high photothermal conversion efficiency. Moreover, the CP‐NPs display effective cellular uptake and cytoplasmic translocation from lysosomes, as well as effective tumor accumulation, thus promoting severe light‐triggered damage caused by favorable reactive oxygen species (ROS) generation and potent hyperthermia. Thus, CP‐NPs achieve photoactive cell damage through their photoconversion ability for synergistic PDT/PTT treatment with tumor ablation. The proof‐of‐concept design of D–A‐type conjugated‐polymer nanoparticles with ideal photophysical characteristics provides a general approach to afford potent photoactive cancer therapy.     

Achieving High‐Performance Photothermal and Photodynamic Effects upon Combining D–A Structure and Nonplanar Conformation

Various organic nanoagents have been developed for photothermal therapy (PTT) and photodynamic therapy (PDT) under near‐infrared (NIR) irradiation. Among them, small molecule‐based nanoagents are very attractive due to their advantages of well‐defined chemical structures, high purity, good reproducibility, and easy processability. However, only a few small molecule‐based nanoagents have been developed for PDT under NIR irradiation. Moreover, the mechanism of PDT under NIR is still elusive. Herein, a semiconducting small molecule (BTA) with donor–acceptor–donor structure and twisted conformation is developed for PDT/PTT under NIR irradiation. A large π‐conjugated electron‐deficient unit is used as the core to couple with two electron‐donating units, ensuring the strong absorption under 808 nm. Moreover, the donor–acceptor structures and twisted conformation can reduce the energy gap between the singlet and triplet states (?E_ST) to afford effective intersystem crossing, beneficial for reactive oxygen species generation. The mechanism is probed by experimental and theoretical evidence. Moreover, the BTA nanoparticles exhibit excellent biocompatibility and PTT/PDT in vitro performance under NIR irradiation. This provides a strategy for designing highly efficient PDT/PTT molecular materials.     

8.78% Efficient All‐Polymer Solar Cells Enabled by Polymer Acceptors Based on a B←N Embedded Electron‐Deficient Unit

In the field of all‐polymer solar cells (all‐PSCs), all efficient polymer acceptors that exhibit efficiencies beyond 8% are based on either imide or dicyanoethylene. To boost the development of this promising solar cell type, creating novel electron‐deficient units to build high‐performance polymer acceptors is critical. A novel electron‐deficient unit containing B←N bonds, namely, BNIDT, is synthesized. Systematic investigation of BNIDT reveals desirable properties including good coplanarity, favorable single‐crystal structure, narrowed bandgap and downshifted energy levels, and extended absorption profiles. By copolymerizing BNIDT with thiophene and 3,4‐difluorothiophene, two novel conjugated polymers named BN‐T and BN‐2fT are developed, respectively. It is shown that these polymers possess wide absorption spectra covering 350–800 nm, low‐lying energy levels, and ambipolar film‐transistor characteristics. Using PBDB‐T as the donor and BN‐2fT as the acceptor, all‐PSCs afford an encouraging efficiency of 8.78%, which is the highest for all‐PSCs excluding the devices based on imide and dicyanoethylene‐type acceptors. Considering that the structure of BNIDT is totally different from these classical units, this work opens up a new class of electron‐deficient unit for constructing efficient polymer acceptors that can realize efficiencies beyond 8% for the first time.     

Functionalized NIR‐II Semiconducting Polymer Nanoparticles for Single‐cell to Whole‐Organ Imaging of PSMA‐Positive Prostate Cancer

Development of molecular probes holds great promise for early diagnosis of aggressive prostate cancer. Here, 2‐[3‐(1,3‐dicarboxypropyl) ureido] pentanedioic acid (DUPA)‐conjugated ligand and bis‐isoindigo‐based polymer (BTII) are synthesized to formulate semiconducting polymer nanoparticles (BTII‐DUPA SPN) as a prostate‐specific membrane antigen (PSMA)‐targeted probe for prostate cancer imaging in the NIR‐II window. Insights into the interaction of the imaging probes with the biological targets from single cell to whole organ are obtained by transient absorption (TA) microscopy and photoacoustic (PA) tomography. At single‐cell level, TA microscopy reveals the targeting efficiency, kinetics, and specificity of BTII‐DUPA SPN to PSMA‐positive prostate cancer. At organ level, PA tomographic imaging of BTII‐DUPA SPN in the NIR‐II window demonstrates superior imaging depth and contrast. By intravenous administration, BTII‐DUPA SPN demonstrates selective accumulation and retention in the PSMA‐positive tumor, allowing noninvasive PA detection of PSMA overexpressing prostate tumors in vivo. The distribution of nanoparticles inside the tumor tissue is further analyzed through TA microscopy. These results collectively demonstrate BTII‐DUPA SPN as a promising probe for prostate cancer diagnosis by PA tomography.     

Selenium‐Doped Cathodes for Lithium–Organosulfur Batteries with Greatly Improved Volumetric Capacity and Coulombic Efficiency

For the first time a new strategy is reported to improve the volumetric capacity and Coulombic efficiency by selenium doping for lithium–organosulfur batteries. Selenium‐doped cathodes with four sulfur atoms and one selenium atom (as the doped heteroatom) in the confined structure are designed and synthesized; this structure exhibits greatly improved volumetric/areal capacities, and a Coulombic efficiency of almost 100% for highly stable lithium–organosulfur batteries. The doping of Se significantly enhances the electronic conductivity of battery electrodes by a factor of 6.2 compared to pure sulfur electrodes, and completely restricts the production of long‐chain lithium polysulfides. This allows achievement of a high gravimetric capacity of 700 mAh g^?1 close to its theoretical mass capacity, an exceptional volumetric capacity of 2457 mAh cm^?3, and excellent capacity retention of 92% after 400 cycles. Shuttle effect is efficiently weakened since no long‐chain polysulfides are detected from in situ UV/vis results throughout the entire cycling process arising from selenium doping, which is theoretically confirmed by density functional theory calculations.     

Conjugated Donor–Acceptor Terpolymers Toward High‐Efficiency Polymer Solar Cells

The development of conjugated alternating donor–acceptor (D–A) copolymers with various electron‐rich and electron‐deficient units in polymer backbones has boosted the power conversion efficiency (PCE) over 17% for polymer solar cells (PSCs) over the past two decades. However, further enhancements in PCEs for PSCs are still imperative to compensate their imperfect stability for fulfilling practical applications. Meanwhile development of these alternating D–A copolymers is highly demanding in creative design and syntheses of novel D and/or A monomers. In this regard, when being possible to adopt an existing monomer unit as a third component from its libraries, either a D′ unit or an A′ moiety, to the parent D–A type polymer backbones to afford conjugated D–A terpolymers, it will give a facile and cost‐effective method to improve their light absorption and tune energy levels and also interchain packing synergistically. Moreover, the rationally controlled stoichiometry for these components in such terpolymers also provides access for further fine‐tuning these factors, thus resulting in high‐performance PSCs. Herein, based on their unique features, the recent progress of conjugated D–A terpolymers for efficient PSCs is reviewed and it is discussed how these factors influence their photovoltaic performance, for providing useful guidelines to design new terpolymers toward high‐efficiency PSCs.     

Efficient Nonfullerene Polymer Solar Cells Enabled by a Novel Wide Bandgap Small Molecular Acceptor

A wide bandgap small molecular acceptor, SFBRCN, containing a 3D spirobifluorene core flaked with a 2,1,3‐benzothiadiazole (BT) and end‐capped with highly electron‐deficient (3‐ethylhexyl‐4‐oxothiazolidine‐2‐yl)dimalononitrile (RCN) units, has been successfully synthesized as a small molecular acceptor (SMA) for nonfullerene polymer solar cells (PSCs). This SMA exhibits a relatively wide optical bandgap of 2.03 eV, which provides a complementary absorption to commonly used low bandgap donor polymers, such as PTB7‐Th. The strong electron‐deficient BT and RCN units afford SFBRCN with a low‐lying LUMO (lowest unoccupied molecular orbital) level, while the 3D structured spirobifluorene core can effectively suppress the self‐aggregation tendency of the SMA, thus yielding a polymer:SMA blend with reasonably small domain size. As the results of such molecular design, SFBRCN enables nonfullerene PSCs with a high efficiency of 10.26%, which is the highest performance reported to date for a large bandgap nonfullerene SMA.     

Improved Performance of All‐Polymer Solar Cells Enabled by Naphthodiperylenetetraimide‐Based Polymer Acceptor

A new polymer acceptor, naphthodiperylenetetraimide‐vinylene (NDP‐V), featuring a backbone of altenating naphthodiperylenetetraimide and vinylene units is designed and applied in all‐polymer solar cells (all‐PSCs). With this polymer acceptor, a new record power‐conversion efficiencies (PCE) of 8.59% has been achieved for all‐PSCs. The design principle of NDP‐V is to reduce the conformational disorder in the backbone of a previously developed high‐performance acceptor, PDI‐V, a perylenediimide‐vinylene polymer. The chemical modifications result in favorable changes to the molecular packing behaviors of the acceptor and improved morphology of the donor–acceptor (PTB7‐Th:NDP‐V) blend, which is evidenced by the enhanced hole and electron transport abilities of the active layer. Moreover, the stronger absorption of NDP‐V in the shorter‐wavelength range offers a better complement to the donor. All these factors contribute to a short‐circuit current density (J _sc) of 17.07 mA cm^?2. With a fill factor (FF) of 0.67, an average PCE of 8.48% is obtained, representing the highest value thus far reported for all‐PSCs.     

Conjugated Polymer Photovoltaic Materials with Broad Absorption Band and High Charge Carrier Mobility

Polymer solar cells (PSCs) have attracted great attention in recent years because of their advantages of easy fabrication, low cost, light weight, and potential for flexible devices. However, the power conversion efficiency (PCE) of the PSCs needs to be improved for future commercial applications. Factors limiting the PCE of the PSCs include the low exploitation of sunlight due to the narrow absorption band of conjugated polymers, and the low charge‐transport efficiency in the devices due to the lower charge‐carrier mobility of the polymer photovoltaic materials. In this Research News article, recent progress in new conjugated polymer photovoltaic materials fabricated by our group and others is reviewed, including polythiophene (PT) and poly(thienylene vinylene) derivatives with conjugated side chains for a broad absorption band, crosslinked PT derivatives with conjugated bridges for higher hole mobility, and low‐bandgap donor–acceptor copolymers for broad, red‐shifted absorption to match the solar spectrum.     

新型三元聚合物给体材料的合成及在有机太阳能电池中的应用

以吡咯并[3,4-c]吡咯二酮(DPP)为A单元,苯并[1,2-b∶4,5-b′]二噻吩(BDT)和萘为D单元,合成了一种新型2D/A型三元共轭聚合物太阳能电池给体材料(PDPP-BDT-NT),通过核磁共振氢谱(1 H NMR)对其结构进行了表征,通过热重分析、紫外-可见吸收光谱(UV-Vis)、循环伏安法对其热学性质、光物理性能及能级结构进行了研究。PDPP-BDT-NT具有较好的热稳定性,热分解的温度为401℃,有较宽的吸收光谱,可覆盖300~900nm,最高占据轨道(HOMO)能级为-5.35eV。以聚合物PDPP-BDT-NT为给体材料,PC60BM为受体材料,制备了一系列有机聚合物太阳能电池,在大气质量(AM)为1.5G,功率为100mW·cm-2模拟的太阳光照射下,有机聚合物太阳能电池的光电转化效率(PCE)可达2.09%。甲醇处理后,有机聚合物太阳能电池的PCE可达2.34%。     

Design of a New Small‐Molecule Electron Acceptor Enables Efficient Polymer Solar Cells with High Fill Factor

Improving the fill factor (FF) is known as a challenging issue in organic solar cells (OSCs). Herein, a strategy of extending the conjugated area of end‐group is proposed for the molecular design of acceptor–donor–acceptor (A–D–A)‐type small molecule acceptor (SMA), and an indaceno[1,2‐b:5,6‐b′]dithiophene‐based SMA, namely IDTN, by end‐capping with the naphthyl fused 2‐(3‐oxocyclopentylidene)malononitrile is synthesized. Benefiting from the π‐conjugation extension by fusing two phenyls, IDTN shows stronger molecular aggregation, more ordered packing structure, thus over one order of magnitude higher electron mobility relative to its counterpart. By utilizing the fluorinated polymer (PBDB‐TF) as the electron donor, the corresponding device exhibits a high efficiency of 12.2% with a record‐high FF of 0.78, which is approaching the theoretical limit of OSCs. Compared with the reference molecule, such a high FF in the IDTN system can be mainly attributed to the more ordered π–π packing of acceptor aggregates, higher domain purity and symmetric carrier transport in the blend. Hence, enlarging the conjugated area of the terminal‐group in these A–D–A‐type SMAs is a promising approach not only for enhancing the electron mobility, but also for improving the blend morphology, and both of them are conducive to the fill‐factor breakthrough.     

Optimized Fibril Network Morphology by Precise Side‐Chain Engineering to Achieve High‐Performance Bulk‐Heterojunction Organic Solar Cells

A polymer fibril assembly can dictate the morphology framework, in forming a network structure, which is highly advantageous in bulk heterojunction (BHJ) organic solar cells (OSCs). A fundamental understanding of how to manipulate such a fibril assembly and its influence on the BHJ morphology and device performance is crucially important. Here, a series of donor–acceptor polymers, PBT1‐O, PBT1‐S, and PBT1‐C, is used to systematically investigate the relationship between molecular structure, morphology, and photovoltaic performance. The subtle atom change in side chains is found to have profound effect on regulating electronic structure and self‐assembly of conjugated polymers. Compared with PBT1‐O and PBT1‐S, PBT1‐C‐based OSCs show much higher photovoltaic performance with a record fill factor (FF) of 80.5%, due to the formation of optimal interpenetrating network morphology. Such a fibril network strategy is further extended to nonfullerene OSCs using a small‐molecular acceptor, which shows a high efficiency of 12.7% and an FF of 78.5%. The results indicate the formation of well‐defined fibrillar structure is a promising approach to achieving a favorable morphology in BHJ OSCs.     

Fine‐Tuning the Energy Levels of a Nonfullerene Small‐Molecule Acceptor to Achieve a High Short‐Circuit Current and a Power Conversion Efficiency over 12% in Organic Solar Cells

Organic solar cell optimization requires careful balancing of current–voltage output of the materials system. Here, such optimization using ultrafast spectroscopy as a tool to optimize the material bandgap without altering ultrafast photophysics is reported. A new acceptor–donor–acceptor (A–D–A)‐type small‐molecule acceptor NCBDT is designed by modification of the D and A units of NFBDT. Compared to NFBDT, NCBDT exhibits upshifted highest occupied molecular orbital (HOMO) energy level mainly due to the additional octyl on the D unit and downshifted lowest unoccupied molecular orbital (LUMO) energy level due to the fluorination of A units. NCBDT has a low optical bandgap of 1.45 eV which extends the absorption range toward near‐IR region, down to ≈860 nm. However, the 60 meV lowered LUMO level of NCBDT hardly changes the V_oc level, and the elevation of the NCBDT HOMO does not have a substantial influence on the photophysics of the materials. Thus, for both NCBDT‐ and NFBDT‐based systems, an unusually slow (≈400 ps) but ultimately efficient charge generation mediated by interfacial charge‐pair states is observed, followed by effective charge extraction. As a result, the PBDB‐T:NCBDT devices demonstrate an impressive power conversion efficiency over 12%—among the best for solution‐processed organic solar cells.     

Synthesis, characterization, and nonlinear optical properties of donor–acceptor conjugated polymers and polymer/Ag nanocomposites

Two new donor–acceptor (D–A) conjugated polymers P1 and P2 containing 3,4-didodecyloxythiophene and 1,3,4-oxadiazole units are synthesized via Wittig reaction methodology. Cyclic voltammetry studies reveal that the polymers are both p and n dopable, and possess low-lying LUMO energy levels (?3.34?eV for P1 and ?3.46?eV for P2) and high-lying HOMO energy levels (?5.34?eV for P1 and ?5.27?eV for P2). The optical band gap of the polymers is in the range of 2.25–2.29?eV, calculated from the onset absorption edge. The polymers emit orange to yellow light in the film state when irradiated with a UV light. The synthesized polymers are used to prepare polymer nanocomposites with different wt% of silver nanoparticles. The polymer nanocomposites are characterized by UV–Vis absorption spectroscopy, field emission scanning electron microscopy, and thermogravimetric analysis. Both polymers and polymer/Ag nanocomposites show good thermal stability with onset decomposition temperature around 300?°C under nitrogen atmosphere. The nonlinear optical properties of polymers and polymer/Ag nanocomposites are measured by Z-scan technique. Both polymers and polymer nanocomposites show a good optical limiting behavior. Nearly five times enhancement in the nonlinear optical properties is observed for polymer/Ag nanocomposites. The value of effective two-photon absorption coefficient (β) is in the order of 10^?10–10^?11?m/W. These results indicate that the synthesized polymers (P1 and P2) and their Ag nanocomposites are expected to be good candidates for application in photonic devices.     

Characterization of polyacrylate membrane-coated fibers used in chemical absorption studies with programmed thermal treatment and FT-IR microscopy

A polyacrylate (PA) film was coated onto a fused-silica fiber as a permeation membrane in a membrane-coated fiber (MCF) technique and a solid-phase microextraction technique. The molecular changes of the PA membrane after different temperature treatments were studied with FT-IR microscopy. The absorption bands of the PA aliphatic backbone at 2902, 2795, and 2740 cm(-)(1) remained unchanged over the elevated thermal treatments, indicating that the polymer backbone was stable over these conditions. The spectra of the PA membrane remained unchanged when the thermal treatment temperature was under 150 degrees C. When the temperature was 250 degrees C, the O-H stretching band in the -COOH groups of the poly(acrylic acid) at 3315 cm(-)(1) was significantly reduced. When the temperature was higher than 280 degrees C, this O-H band disappeared. These evidences suggested that the PA membrane underwent dehydroxyl reaction to form an anhydride when the thermal treatments were higher than 250 degrees C. Thermal treatments of a deuterated PA MCF confirmed the anhydride formation mechanism. The anhydride formation explained the absorption property of PA MCFs in GC applications where they must be preconditioned at 300 degrees C. The absorption data suggest that a PA fiber does not preferably absorb polar compounds (with permanent dipole moment); instead, it absorbs preferably aromatic compounds.